Conventionally, this kind of one-main-pipe type centralized lubrication apparatus, as disclosed in, for example, the Japanese Utility Model Publication Gazette No. Sho 52-150 and shown in FIG. 17, comprises; an electric-operated pump device provided with a pump element A communicating with a tank T in which lubricating oil is charged and a pilot operated directional control valve B; one main oil feed pipe F connected to a discharge port P of the electric-operated pump device, and a plurality of distributors G connected to the main oil feed pipe F, the directional control valve B being movably disposing therein, a spool C having first and second lands a and b, and being provided at one axial side of the spool C with a spring D, and at the other axial side with a pilot chamber E, a discharge passage H which communicates with the discharge side of the pump element A and with a discharge port P through the one main pipe, and a pilot passage I for communicating the pilot chamber E with the discharge passage H and a depressurized passage J for allowing the pilot chamber E to be open at the tank T through the spool C.
Each distributor G is provided; with two first and second chambers L and M partitioned by a valve body K, the first chamber L communicating with the main pipe F; and with a measuring cylinder N having a measuring piston n selectively communicating with the respective chambers L and M following the movement of the valve K, the first chamber L communicating with the main pipe F is pressurized to move the valve K so as to discharge lubricating oil in the second chamber M toward the lubrication parts, lubricating oil supplied from the main pipe F is introduced into the cylinder N and measured thereby, and thereafter the main pipe F side is depressurized so that the valve K is restored by operation of a spring S and the lubricating oil measured by the cylinder N is supplied to the second chamber M by operation of measuring piston, thereby preparing the next oil feed.
In the above-mentioned construction, when the pump element A stops, the spool C is held at the position in FIG. 17 by being biased by the spring D, a first land a of spool C closes the discharge passage H, the second land b shuts off communication of the pilot chamber E with the depressurized passage J, and the main pipe F is open to the tank T through the passage J so as to be depressurized. The pump element A starts to be driven from the above-mentioned stop condition, whereby the lubricating oil discharged from the pump element A is supplied from the discharge passage H to the pilot chamber E through the pilot passage I because the discharge passage H is closed by the first land a. Hence, pressure in the pilot chamber E rises so that the entire spool C moves against the spring D, the second land b closes the depressurized passage J and the discharge passage H is open, and the lubricating oil is supplied to each distributor G and then to lubricating parts therethrough as the above operation. Furthermore, after the lubricating oil is supplied to each distributor G so that oil feed to the lubricating parts is completed, the pump element A is stopped, whereby the spool C is restored by the spring D. Hence, the main pipe F is open at the depressurized passage J and depressurized thereat, the valve K of each distributor G is restored by operation of the spring S, and the measured lubricating oil is supplied to the second chamber M, thereby being prepared for the next oil feed.
In the one-main-pipe type centralized lubrication appratus constructed as above-mentioned, since the lubricating oil is supplied to each distributor G and measured therein, pressurization and depressurization at the main pipe G side must be repeated, and in a case where the pilot operated directional control valve B switched by starting or stopping the pump element A as the aforesaid electric-operated pump device, it is not problematical when lubricating oil or grease of low viscosity is used as the lubricant, but when a lubricating oil of high viscosity is used or the apparatus is used in low temperature condition, even if the pump element A stops, pressure drop at the pilot chamber E of pilot operated directional control valve B is carried out by a leak of oil from the pilot chamber A, so that a time delay is created so as not to carry out quick depressurization, thereby creating the problem in that an oil feed cycle from each distributor G is hindered.
On the other hand, the distributors are each provided with a measuring cylinder N disposed perpendicularly to the moving direction of the valve K, and improved distributors are proposed which dispose the valve and measuring piston in series so as to enable the valve body to be compact. Such distributor is disclosed in, for example, the U.S. Pat. No. 3,145,803 and shown in FIG. 18, wherein a cylinder bore U communicating with an oil feed passage Q and an oil discharge passage R is formed in a valve body O having the oil feed passage Q and oil discharge passage R, a measuring piston V is reciprocably provided in the cylinder bore U, the cylinder bore U is partitioned into a measuring chamber e and a back chamber f by the piston V, a valve W is disposed at the oil feed passage Q side of cylinder bore U, a spring X is interposed between the valve W and the piston V, and in the valve body O is formed an oil passage Y extending from the oil feed passage Q to the back chamber f.
The oil feed passage Q at each distributor constructed as the above-mentioned is connected to the main pipe communicating with a pump and lubricating oil is supplied to the oil feed passage Q by driving the pump, whereby the valve W at each distributor is forwardly moved to supply to the back chamber f at the cylinder bore U the lubricating oil supplied to the oil feed passage Q and the piston V is forwardly moved following the supply of lubricating oil, thereby feeding lubricating oil of a predetermined amount measured at the measuring chamber e from the oil discharge passage R to lubricating parts, such as a machine tool. After oil feed by each distributor is completed, the pump stops its drive to depressurize the main pipe connected with the oil feed passage Q. Hence, the valve body W is backwardly moved to cut off the communication of oil feed passage Q with the oil passage Y, and simultaneously therewith the piston V is backwardly moved by the spring X, so that the lubricating oil supplied to the back chamber f side is introduced into the measuring chamber e and measured therein for the next oil feed.
In the distributor constructed as above-mentioned, the oil passage Y for communicating the oil feed passage Q with the back chamber f at the piston V forms a vertical passage at the lateral side of cylinder bore U at the valve body O and a horizontal passage for communicating the vertical passage with the oil feed passage Q and back chamber f, so that the passage machining is very complicated. Also, the vertical and horizontal passages constituting the oil passage Y must perforate the outer surface of valve body O, whereby after the passage machining, a plug (not shown) must be mounted for closing each perforating portion. Hence, when the valve body W, piston V and spring X are assembled with the valve body O, whereby a problem is created in that the assembly efficiency is poor to thus complicating automatic assembly; thus the apparatus is expensive to produce as a whole.